A liquid crystal display (LCD) includes an LCD panel formed with liquid crystal cells and pixel elements with each associating with a corresponding liquid crystal cell. These pixel elements are substantially arranged in the form of a matrix having gate lines in rows and data lines in columns. The LCD panel is driven by a driving circuit including a gate driver and a data driver. The gate driver generates a plurality of gate signals (scanning signals) sequentially applied to the gate lines for sequentially turning on the pixel elements row-by-row. The data driver generates a plurality of source signals (data signals), i.e., sequentially sampling image signals, simultaneously applied to the data lines in conjunction with the gate signals applied to the gate lines for aligning states of the liquid crystal cells on the LCD panel to control light transmittance therethrough, thereby displaying an image on the LCD.
In such a driving circuit, a shift register is utilized in the gate driver to generate the plurality of gate signals for sequentially driving the gate lines. To lower down costs, there have been efforts to integrate the shift register and the gate driver into an LCD panel. One of the efforts, for example, is to fabricate the shift register and the gate driver on a glass substrate of the LCD panel, namely, the gate on array (GOA) arrangement, using amorphous silicon (a-Si) thin film transistors (TFTs), and/or low temperature polycrystalline silicon (LTPS) TFTs.
Generally, a shift register having multiple stages is designed such that in operation there are some TFTs that are turned on for a long period of time for the purpose of discharges. Additionally, such a shift register is usually supplied with two or more clock signals to substantially shift an output signal of a stage from its input signal that is an output signal of its immediately prior stage, thereby generating of a plurality of sequentially shifted output signals. If the two or more clock signals have a same frequency that is very high, some TFTs in the shift register may frequently be turned on during operation. However, when voltages are continually or frequently applied to TFTs made from a-Si and/or LTPS material for a long period of time, the characteristics of the TFTs may deteriorate due to stress thereon and thus the TFTs may not function properly, thereby reducing the reliability of the shift register. For the shift register operating reliably and normally, a plurality of pull-down circuit sets is applied to reduce the stress. This makes the GOA design of an LCD panel very complicate.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.